Vacuum-actuated exhaust valve project (Axleback)
 

Hi everyone,

You might remember me from the project where I took a stock muffler and modified it with a electronic exhaust valve.
http://www.ft86club.com/forums/showthread.php?t=111280

Well, this time, I took things a step further! Since the preivous muffler rusted out in an uncontrollable fashion, I bought another one (OEM) and decided to go with a vacuum-actuated valve.

I bought it off Aliexpress and I have to say, the quality is more than decent! Been running it for two months with no issues while the previous, electronically-activated one, was less reliable. I often had to disassemble the motor to put all the gears back in place.

So, let's get to it:

STEP 1 : Modifying the muffler.

Once again, I called my friend Julien to help me with this. He's a brilliant mechanic currently working for Gillet Motorsport, the only Belgian car "manufacturer" there's left! Americans might have seen a Gillet Vertigo at last year's Pikes Peak, driven by Vanina Ickx, Jacky Ickx's daughter.

http://petrolistes.com/wp-content/up...3568285869.jpg

Some might argue the exhaust path is not optimum, and they'd be right. The sole purpose here is to liven up the exhaust by making it a bit louder. And I don't think the stock exhaust, aside from its weight, is badly designed regarding exhaust flow.

http://petrolistes.com/wp-content/up...3568364322.jpg

Exhaust upside down so you can see the valve.


STEP 2 : Finding a vacuum source


I chose to T the brake booster line. And so far, even in 'spirited' conditions, I haven't experienced any brake fade at all.

http://petrolistes.com/wp-content/up...3568528904.jpg

STEP 3 : The control device.

There are three modes. Open, closed and active.
The last one works as this: when the engine is not under load, vacuum pressure is created in the intake manifold. When you apply throttle, vacuum decreases which open the valve. The valve type is therefore a normally open one.


The three modes are made possible thanks to 2 solenoids and a on-off-on switch.

Here's the solenoids wiring (still in ghetto beta style):
http://petrolistes.com/wp-content/up...3568932104.jpg

And the switch is located between the traction control and ESP switches.
Not the cleanest, but clean enough for me.
In daylight, the color of the switch and the oem module are nearly identical.

http://petrolistes.com/wp-content/up...3569028735.jpg

O = closed
|| = open
| = active.
I think that kinda make sense.

THE RESULTS :

[ame]https://www.youtube.com/watch?v=1GuWckCCcOg[/ame]

My opinion :
I absolutely love it.
I especially like the active mode. This is what I was after and I'm not disappointed. The active mode feels like it comes from the factory. And makes the car feel more... I don't know, refined?
Anyone can be loud. When you have a full exhaust, you sound like you have a full exhaust, like the car is tuned. With the active mode, it seems more "powerful", if that makes any sense. Like when you see a TT-RS or RS3 passing by. They don't make that much sound but when they send it, you're like "oh crap", all hell breaks loose. That's the effect my car now does, at least, kind of, still while going half the speed of course...

Thanks.
If you have any question, feel free to ask!

can you explain how the different modes get activated? does 'open' just pull vacuum all the time?

Good piece of work. Nice presentation. - :thumbsup:


humfrz

The switch powers the two solenoids.
The solenoids are in a normally-closed configuration.

On the closed position, no current is brought to the solenoids so they stay closed. To close the valve, you first need to go on the active position for half of second so you can build pressure in the tube that goes from the intake to the valve.

On the active position, the solenoid on the right opens. Which basically makes the system just a cable from the intake to the valve.

On the open position, the solenoid on the left opens so the valve is simply disconnected from the system and since it's a normally-open design, it just stays open.

Cool thing is, it's not as loud as a muffler delete and the fact that the exhaust gases takes a third path, when the meet at the tip, I can't really explain why but the sounds feel smoother than when I had a muffler delete.

And I though it was an interesting project Ahah !

it is definitely interesting to me! i'm still mulling over how to build my own using a vacuum/electric hybrid setup so i don't have to build vacuum for the open mode.

probably something i'll try in the future, but i've got a bothersome truck with rust issues, and a few dozen other projects demanding attention.

It would be cool to use canbus to monitor load and use a lookup table to determine what voltage to send to the solenoid for the given load. It could all be done with an Arduino and canbus shield. This would have lots of benefits over using the vacuum. For example you could use a long press on the KPH/MPH button to disable the bypass completely if you need it to stay quiet.

I was actually thinking of using the gas pedal position to trigger the valving, though rpm- based is likely better. I've already got some momentary buttons set up for some random future use by the shifter to use for different modes

The ECU calculates load based on throttle position, gear, RPM, etc. If you tie it to load you don’t have to reinvent the wheel.

I think a valve controlled by canbus data would be the best.
Throttle position, load,
The only complain I might have with the vacuum actuated valve is when in active mode, when you just start from a standstill, the engine is under "heavy" load at low RPM which, generally with a four banger, sounds like absolute crap. Same things generally when you're cruising.

Which a canbus-driven valve, you could avoid that. But I think, everytime you could with an electronic solution over a mechanical one, you're sacrificing some reliability.

I could give these a go one of these days. They look like they work like an intake butterfly valve
https://www.aliexpress.com/item/3283...chweb201603_60

I love the active exhaust mode! Does it hold up in the winter and snow?

It'd be kinda cool to see dyno of a pull open and another closed. Who knows maybe it make more torque at the low end and you can pinpoint when to open to maximize.

Update: so far so good avec 18 months of daily driving. You only need a handy mechanic to make the soldering work reliable. The aliexpress valve has been flawless in both summer and winter.

Great job. I remember my e46 had this from the factory. Everyone would unplug the hose from the muffler and shove a golf tee into it so it would be open all the time. "Golf tee mod".